Vitamin D Calculator

Vitamin D is unusual among vitamins: your skin makes it from sunlight, and it is still one of the most common nutritional shortfalls in the world. Indoor work, sunscreen and high latitudes each cut production, and together they cut it a lot.

What the target is, and what this page does with it

The US Recommended Dietary Allowance (RDA), set by the Institute of Medicine (IOM) in 2010, is the number this page gives you:

The IOM set it assuming almost no sun, so it is a figure to get from food and supplements. That is why skin tone, latitude and season do not change it here. What they change is how much of it the sun could cover instead: above about 37° north or south, the sun sits too low between roughly November and February for the UVB that makes vitamin D to reach the ground, however bright the day looks. Darker skin needs three to four times longer in the same sun.

Why the page does not multiply up a bigger dose

You will find calculators that start at 1,000 IU and multiply by factors for weight, skin, latitude and season. None of those factors come from a guideline. You will also see “40 to 60 IU per kilogram” repeated as a daily need. Run it and an ordinary 80 kg adult lands on 4,000 IU before any adjustment, which is the upper limit. That figure comes from deficiency correction under a doctor, not from everyday maintenance.

Body weight is the one adjustment with real evidence behind it: the same dose raises blood levels less in people with obesity. The Endocrine Society’s 2011 guideline suggested two to three times as much for them. Its 2024 update dropped dosing by weight, and also stopped recommending routine blood tests in healthy adults.

What the 2024 Endocrine Society guideline does recommend

A supplement above the RDA for four groups: children and teens, adults 75 and over, pregnancy, and adults with prediabetes. For other adults under 75 it advises against going beyond the RDA, because the trials found no benefit.

Reference ranges

Blood level (25-hydroxyvitamin D):

The IOM reads under 12 ng/mL (30 nmol/L) as deficient, 12 to 20 as possibly low, and 20 ng/mL (50 nmol/L) or more as enough for almost everyone. Above 50 ng/mL (125 nmol/L) it saw possible harm. Many labs still flag anything under 30, the 2011 Endocrine Society cut-off, which is the main reason two doctors can read the same result differently.

Food sources (NIH): cod liver oil 1,360 IU a tablespoon, farmed rainbow trout 645 IU per 3 oz, sockeye salmon 570 IU, UV-exposed mushrooms 366 IU per half cup, fortified milk about 120 IU a cup, a large egg 44 IU, canned light tuna 40 IU per 3 oz. Oily fish twice a week plus fortified milk gets most people a long way, and a 1,000 IU supplement covers the rest with room to spare.

Sunlight: a full-body exposure to one minimum erythemal dose, just short of visible redness, produces roughly 10,000 to 20,000 IU. That figure is often misread as what a short walk gives you. Five to seven minutes of midday summer sun on fair skin in shorts and a T-shirt is closer to 2,000 IU, because you are exposing about 40% of your skin for about a third of your burn threshold. The Vitamin D Sun Exposure Calculator works this out for your own skin, latitude and season.